Mercury flux to sediments of Lake Tahoe, California–Nevada

We report estimates of mercury (Hg) flux to the sediments of Lake Tahoe, California–Nevada: 2 and 15–20 µg/m²/year in preindustrial and modern sediments, respectively. These values result in a modern to preindustrial flux ratio of 7.5–10, which is similar to flux ratios recently reported for other alpine lakes in California, and greater than the value of 3 typically seen worldwide. We offer plausible hypotheses to explain the high flux ratios, including (1) proportionally less photoreduction and evasion of Hg with the onset of cultural eutrophication and (2) a combination of enhanced regional oxidation of gaseous elemental Hg and transport of the resulting reactive gaseous Hg to the surface with nightly downslope flows of air. If either of these mechanisms is correct, it could lead to local/regional solutions to lessen the impact of globally increasing anthropogenic emissions of Hg on Lake Tahoe and other alpine ecosystems.